Using graphical means, find an amplitude a of oscillations resulting from the superposition of the following oscillations

Question:

Using graphical means, find an amplitude a of oscillations resulting from the superposition of the following oscillations of the same direction:
(a) x1 = 3.0 cos (wt + π/3), x2 = 8.0sin (wt + π/6);
(b) x1 = 3.0 cos wt, x 2 = 5.0 cos (wt + π/4), x3 = 6.0 sin wt.